1. Field of the Invention
This invention relates to the formulation of pharmaceutical compounds. More particularly, the invention relates to stable, pharmaceutically acceptable compositions prepared from boronic acid compounds. The invention also relates to methods for preparing such compositions.
2. Summary of the Related Art
Boronic acid and ester compounds display a variety of pharmaceutically useful biological activities. Shenvi et al., U.S. Pat. No. 4,499,082 (1985), discloses that peptide boronic acids are inhibitors of certain proteolytic enzymes. Kettner and Shenvi, U.S. Pat. No. 5,187,157 (1993); U.S. Pat. No. 5,242,904 (1993); and U.S. Pat. No. 5,250,720 (1993), describe a class of peptide boronic acids that inhibit trypsin-like proteases. Kleeman et al., U.S. Pat. No. 5,169,841 (1992), discloses N-terminally modified peptide boronic acids that inhibit the action of renin. Kinder et al., U.S. Pat. No. 5,106,948 (1992), discloses that certain tripeptide boronic acid compounds inhibit the growth of cancer cells.
More recently, boronic acid and ester compounds have displayed particular promise as inhibitors of the proteasome, a multicatalytic protease responsible for the majority of intracellular protein turnover. Ciechanover, Cell, 79: 13-21 (1994), teaches that the proteasome is the proteolytic component of the ubiquitin-proteasome pathway, in which proteins are targeted for degradation by conjugation to multiple molecules of ubiquitin. Ciechanover also teaches that the ubiquitin-proteasome pathway plays a key role in a variety of important physiological processes.
Adams et al., U.S. Pat. No. 5,780,454 (1998), U.S. Pat. No. 6,066,730 (2000), U.S. Pat. No. 6,083,903 (2000), and U.S. Pat. No. 6,297,217 (2001), hereby incorporated by reference in their entirety, describe peptide boronic ester and acid compounds useful as proteasome inhibitors. The references also describe the use of boronic ester and acid compounds to reduce the rate of muscle protein degradation, to reduce the activity of NF-xcexaB in a cell, to reduce the rate of degradation of p53 protein in a cell, to inhibit cyclin degradation in a cell, to inhibit the growth of a cancer cell, to inhibit antigen presentation in a cell, to inhibit NF-xcexaB dependent cell adhesion, and to inhibit HIV replication. Brand et al., WO 98/35691, teaches that proteasome inhibitors, including boronic acid compounds, are useful for treating infarcts such as occur during stroke or myocardial infarction. Elliott et al., WO 99/15183, teaches that proteasome inhibitors are useful for treating inflammatory and autoimmune diseases.
Unfortunately, alkylboronic acids are relatively difficult to obtain in analytically pure form. For example, Snyder et al., J. Am. Chem. Soc. 80: 3611 (1958), teaches that arylboronic acid compounds readily form cyclic trimeric anhydrides under dehydrating conditions. Also, alkylboronic acids and their boroxines are often air-sensitive. Korcek et al., J. Chem. Soc., Perkin Trans. 2 242 (1972), teaches that butylboronic acid is readily oxidized by air to generate 1-butanol and boric acid. These difficulties limit the pharmaceutical utility of boronic acid compounds, complicating the characterization of pharmaceutical agents comprising boronic acid compounds and limiting their shelf-life.
There is thus a need in the art for improved formulations of boronic acid compounds. Ideally, such formulations would be conveniently prepared, would exhibit enhanced stability and longer shelf life as compared to the free boronic acid compound, and would readily liberate the bioactive boronic acid compound when administered to a subject in need of boronic acid therapy.
The present invention provides stable, pharmaceutically acceptable compositions prepared from boronic acid compounds. The invention also provides methods for preparing such compositions. The invention provides the discovery that lyophilization of an aqueous mixture comprising a boronic acid compound and a compound having at least two hydroxyl groups produces a stable composition that readily releases the boronic acid compound upon dissolution in aqueous media.
In a first aspect, the invention provides boronate ester compounds having formula (1): 
wherein:
P is hydrogen or an amino-group protecting moiety;
R is hydrogen or alkyl;
A is 0, 1, or 2;
R1, R2, and R3 are independently hydrogen, alkyl, cycloalkyl, aryl, or xe2x80x94CH2xe2x80x94R5;
R5, in each instance, is one of aryl, aralkyl, alkaryl, cycloalkyl, heterocyclyl, heteroaryl, or xe2x80x94Wxe2x80x94R6, where W is a chalcogen and R6 is alkyl;
where the ring portion of any of said aryl, aralkyl, alkaryl, cycloalkyl, heterocyclyl, or heteroaryl in R1, R2, R3 or R5 can be optionally substituted; and
Z1 and Z2 together form a moiety derived from a sugar, wherein the atom attached to boron in each case is an oxygen atom.
In a second aspect, the invention provides a composition comprising a compound of formula (2): 
wherein:
P is hydrogen or an amino-group-protecting moiety;
R is hydrogen or alkyl;
A is 0, 1, or 2;
R1, R2, and R3 are independently hydrogen, alkyl, cycloalkyl, aryl, or xe2x80x94CH2xe2x80x94R5;
R5, in each instance, is one of aryl, aralkyl, alkaryl, cycloalkyl, heterocyclyl, heteroaryl, or xe2x80x94Wxe2x80x94R6, where W is a chalcogen and R6 is alkyl;
where the ring portion of any of said aryl, aralkyl, alkaryl, cycloalkyl, heterocyclyl, or heteroaryl in R1, R2, R3 or R5 can be optionally substituted; and
Z3 and Z4 together form a moiety derived from a compound having at least two hydroxyl groups separated by at least two connecting atoms in a chain or ring, said chain or ring comprising carbon atoms and, optionally, a heteroatom or heteroatoms which can be N, S, or O;
in a lyophilized powder.
In a third aspect, the invention provides a method for formulating a boronic acid compound, the method comprising:
(a) preparing an aqueous mixture comprising
(i) a boronic acid compound; and
(ii) a compound having at least two hydroxyl groups separated by at least two connecting atoms in a chain or ring, the chain or ring comprising carbon atoms, and optionally, a heteroatom or heteroatoms which can be N, S, or O; and
(b) lyophilizing the mixture.
In a fourth aspect, the invention provides a method for formulating a boronic acid compound, the method comprising:
(a) preparing a boronic acid anhydride compound;
(b) mixing the boronic acid anhydride compound with water and a compound having at least two hydroxyl groups separated by at least two connecting atoms in a chain or ring, the chain or ring comprising carbon atoms, and, optionally, a heteroatom or heteroatoms which can be N, S, or O to produce an aqueous mixture; and
(c) lyophilizing the mixture.
In a fifth aspect, the invention provides compositions prepared by the methods of the invention.
In a sixth aspect, the invention provides boronic acid anhydride compounds useful in the methods of the invention.
The invention provides stable, pharmaceutically acceptable compositions prepared from boronic acid compounds and methods for preparing the compositions. The invention also provides novel boronate ester compounds. The invention further provides boronic acid anhydride compounds useful in the methods of the invention.
The patent and scientific literature referred to herein establishes knowledge that is available to those with skill in the art. The issued patents, applications, and references that are cited herein are hereby incorporated by reference to the same extent as if each was specifically and individually indicated to be incorporated by reference. In the case of inconsistencies, the present disclosure will prevail.
For purposes of the present invention, the following definitions will be used:
As used herein, the terms xe2x80x9cformulatexe2x80x9d and xe2x80x9cformulationxe2x80x9d refer to the preparation of a boronic acid compound in a form suitable for administration to a mammalian subject, preferably a human. Often, formulation of the boronic acid compound comprises addition of pharmaceutically acceptable excipients, diluents, or carriers. In some embodiments, formulation of the boronic acid compound comprises formation of a chemical derivative of the boronic acid compound, preferably formation of a boronate ester. The term xe2x80x9cformulationxe2x80x9d refers to any form commonly used for pharmaceutical administration, including solids, liquids, suspensions, creams, and gels. For purposes of the present invention, the formulation is preferably a lyophilized powder.
As used herein, the term xe2x80x9clyophilized powderxe2x80x9d refers to any solid material obtained by lyophilization of an aqueous mixture.
By xe2x80x9cstable formulationxe2x80x9d is meant any formulation having sufficient stability to have utility as a pharmaceutical agent. Preferably, the formulation has sufficient stability to allow storage at a convenient temperature, preferably between 0xc2x0 C. and 40xc2x0 C., for a reasonable period of time, preferably longer than one month, more preferably longer than three months, even more preferably longer than six months, and most preferably longer than one year.
As employed herein, the term xe2x80x9cboronic acidxe2x80x9d refers to any chemical compound comprising a xe2x80x94B(OH)2 moiety. Snyder et al., J. Am. Chem. Soc. 80: 3611 (1958), teaches that arylboronic acid compounds readily form oligomeric anhydrides by dehydration of the boronic acid moiety. Thus, unless otherwise apparent from context, the term xe2x80x9cboronic acidxe2x80x9d is expressly intended to encompass free boronic acids, oligomeric anhydrides, including, but not limited to, dimers, trimers, and tetramers, and mixtures thereof.
As employed herein, the term xe2x80x9ccompound having at least two hydroxyl groupsxe2x80x9d refers to any compound having two or more hydroxyl groups. For purposes of the present invention, the two hydroxyl groups are preferably separated by at least two connecting atoms, preferably from about 2 to about 5 connecting atoms, more preferably 2 or 3 connecting atoms. The connecting atoms may be in a chain or a ring, the chain or ring comprising carbon atoms and, optionally, a heteroatom or heteroatoms which can be N, S, or O. For convenience, the term xe2x80x9cdihydroxy compoundxe2x80x9d may be used to refer to a compound having at least two hydroxyl groups, as defined above. Thus, as employed herein, the term xe2x80x9cdihydroxy compoundxe2x80x9d is not intended to be limited to compounds having only two hydroxyl groups.
As employed herein, the term xe2x80x9camino-group protecting moietyxe2x80x9d refers to any group used to derivatize an amino group, especially an N-terminal amino group of a peptide or amino acid. Such groups include, without limitation, alkyl, acyl, alkoxycarbonyl, aminocarbonyl, and sulfonyl moieties. However, the term xe2x80x9camino-group protecting moietyxe2x80x9d is not intended to be limited to those particular protecting groups that are commonly employed in organic synthesis, nor is it intended to be limited to groups that are readily cleavable.
The term xe2x80x9cchalcogenxe2x80x9d as employed herein refers to the elements oxygen or sulfur.
The term xe2x80x9calkylxe2x80x9d as employed herein refers to straight and branched chain aliphatic groups having from 1 to 12 carbon atoms, preferably 1-8 carbon atoms, more preferably 1-6 carbon atoms, and still more preferably 1-4 carbon atoms, which may be optionally substituted with one, two or three substituents. Unless otherwise explicitly stated, the term xe2x80x9calkylxe2x80x9d is meant to include saturated, unsaturated, and partially unsaturated aliphatic groups. When unsaturated groups are particularly intended, the terms xe2x80x9calkenylxe2x80x9d or xe2x80x9calkynylxe2x80x9d will be used. When only saturated groups are intended, the term xe2x80x9csaturated alkylxe2x80x9d will be used. Preferred saturated alkyl groups include, without limitation, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, and hexyl.
The term xe2x80x9ccycloalkylxe2x80x9d as employed herein includes saturated and partially unsaturated cyclic hydrocarbon groups having 3 to 12 carbons, preferably 3 to 8 carbons, and more preferably 3 to 6 carbons, wherein the cycloalkyl group additionally may be optionally substituted. Preferred cycloalkyl groups include, without limitation, cyclopropyl, cyclobutyl, cyclopentyl, cyclopentenyl, cyclohexyl, cyclohexenyl, cycloheptyl, and cyclooctyl.
An xe2x80x9carylxe2x80x9d group is a C6-C14 aromatic moiety comprising one to three aromatic rings, which may be optionally substituted. Preferably, the aryl group is a C6-C10 aryl group. Preferred aryl groups include, without limitation, phenyl, naphthyl, anthracenyl, and fluorenyl. An xe2x80x9caralkylxe2x80x9d or xe2x80x9carylalkylxe2x80x9d group comprises an aryl group covalently linked to an alkyl group, either of which may independently be optionally substituted or unsubstituted. Preferably, the aralkyl group is (C1-C6)alk(C6-C10)aryl, including, without limitation, benzyl, phenethyl, and naphthylmethyl. An xe2x80x9calkarylxe2x80x9d or xe2x80x9calkylarylxe2x80x9d group is an aryl group having one or more alkyl substituents. Examples of alkaryl groups include, without limitation, tolyl, xylyl, mesityl, ethylphenyl, tert-butylphenyl, and methylnaphthyl.
The terms xe2x80x9cheterocyclexe2x80x9d, xe2x80x9cheterocyclicxe2x80x9d, and xe2x80x9cheterocyclylxe2x80x9d refer to any stable ring structure having from about 3 to about 8 atoms, wherein one or more atoms are selected from the group consisting of N, O, and S. The nitrogen and sulfur heteroatoms of the heterocyclic moiety may be optionally oxidized, and the nitrogen atoms may be optionally quaternized. The heterocyclic ring can be attached to its pendant group at any heteroatom or carbon atom that results in a stable formula. The term xe2x80x9cstable compoundxe2x80x9d or xe2x80x9cstable formulaxe2x80x9d is meant to refer to a compound that is sufficiently robust to survive isolation to a useful degree of purity from a reaction mixture and formulation into an efficacious therapeutic agent.
The heterocyclic group may be optionally substituted on carbon at one or more positions with any of the substituents recited above. The heterocyclic group may also independently be substituted on nitrogen with alkyl, aryl, aralkyl, alkylcarbonyl, alkylsulfonyl, arylcarbonyl, arylsulfonyl, alkoxycarbonyl, aralkoxycarbonyl, oxo, or hydroxy, or on sulfur with oxo or lower alkyl. Preferred heterocyclic groups include, without limitation, epoxy, aziridinyl, tetrahydrofuranyl, pyrrolidinyl, piperidinyl, piperazinyl, thiazolidinyl, oxazolidinyl, oxazolidinonyl, and morpholinyl. The heterocyclic group may also be fused to an aryl, heteroaryl, or heterocyclic group. Examples of such fused heterocyles include, without limitation, tetrahydroquinoline and dihydrobenzofuran.
As used herein, the terms xe2x80x9cheteroarylxe2x80x9d and xe2x80x9caromatic heterocylexe2x80x9d refer to groups having 5 to 14 ring atoms, preferably 5, 6, 9, or 10 ring atoms; having 6, 10, or 14 xcfx80 electrons shared in a cyclic array; and having, in addition to carbon atoms, from one to about four, preferably from one to about three, heteroatoms selected from the group consisting of N, O, and S. The heteroaryl group may be optionally substituted on carbon at one or more positions with any of the substituents recited above. Preferred heteroaryl groups include, without limitation, thienyl, benzothienyl, furyl, benzofuryl, dibenzofuryl, pyrrolyl, imidazolyl, pyrazolyl, pyridyl, pyrazinyl, pyrimidinyl, indolyl, quinolyl, isoquinolyl, quinoxalinyl, tetrazolyl, oxazolyl, thiazolyl, and isoxazolyl.
As employed herein, a xe2x80x9csubstitutedxe2x80x9d alkyl, cycloalkyl, aryl, heterocyclyl, or heteroaryl group is one having from one and to about four, preferably from one to about three, more preferably one or two, non-hydrogen substituents. Suitable substituents include, without limitation, halo, hydroxy, oxo, nitro, haloalkyl, alkyl, alkaryl, aryl, aralkyl, alkoxy, aryloxy, amino, acylamino, alkylcarbamoyl, arylcarbamoyl, aminoalkyl, alkoxycarbonyl, carboxy, hydroxyalkyl, alkanesulfonyl, arenesulfonyl, alkanesulfonamido, arenesulfonamido, aralkylsulfonamido, alkylcarbonyl, acyloxy, cyano, and ureido groups. Preferably the substituents are independently selected from the group consisting of C1-C6 alkyl, C3-C8 cycloalkyl, (C1-C6)alkyl(C3-C8)cycloalkyl, C2-C8alkenyl, C2-C8 alkynyl, cyano, amino, C1-C6alkylamino, di(C1-C6)alkylamino, benzylamino, dibenzylamino, nitro, carboxy, carbo(C1-C6)alkoxy, trifluoromethyl, halogen, C1-C6 alkoxy, C6-C10 aryl, (C6-C10)aryl(C1-C6)alkyl, (C6-C10)aryl(C1-C6)alkoxy, hydroxy, C1-C6 alkylthio, C1-C6 alkylsulfinyl, C1-C6 alkylsulfonyl, C6-C10 arylthio, C6-C10 arylsulfinyl, C6-C10 arylsulfonyl, C6-C10 aryl, (C1-C6)alkyl(C6-C10)aryl, and halo(C6-C10)aryl.
The term xe2x80x9chalogenxe2x80x9d or xe2x80x9chaloxe2x80x9d as employed herein refers to chlorine, bromine, fluorine, or iodine.
The term oxo refers to an oxygen atom, which forms a carbonyl when attached to carbon, an N-oxide when attached to nitrogen, and a sulfoxide or sulfone when attached to sulfur.
As herein employed, the term xe2x80x9cacylxe2x80x9d refers to an alkylcarbonyl or arylcarbonyl substituent.
The term xe2x80x9cacylaminoxe2x80x9d refers to an amide group attached at the nitrogen atom. The term xe2x80x9ccarbamoylxe2x80x9d refers to an amide group attached at the carbonyl carbon atom. The nitrogen atom of an acylamino or carbamoyl substituent may be additionally substituted. The term xe2x80x9csulfonamidoxe2x80x9d refers to a sulfonamide substituent attached by either the sulfur or the nitrogen atom. The term xe2x80x9caminoxe2x80x9d is meant to include NH2, alkylamino, arylamino, and cyclic amino groups.
The term xe2x80x9cureidoxe2x80x9d as employed herein refers to a substituted or unsubstituted urea moiety.
In a first aspect, the invention provides boronate ester compounds having formula (1): 
wherein
P is hydrogen or an amino-group protecting moiety;
R is hydrogen or alkyl;
A is 0, 1, or 2;
R1, R2, and R3 are independently hydrogen, alkyl, cycloalkyl, aryl, or xe2x80x94CH2xe2x80x94R5;
R5, in each instance, is one of aryl, aralkyl, alkaryl, cycloalkyl, heterocyclyl, heteroaryl, or xe2x80x94Wxe2x80x94R6, where W is a chalcogen and R6 is alkyl;
where the ring portion of any of said aryl, aralkyl, alkaryl, cycloalkyl, heterocyclyl, or heteroaryl in R1, R2, R3 or R5 can be optionally substituted; and
Z1 and Z2 together form a moiety derived from a sugar, wherein the atom attached to boron in each case is an oxygen atom.
As used herein, the term xe2x80x9cmoiety derived from a sugarxe2x80x9d refers to a moiety formed by removing the hydrogen atoms from two hydroxyl groups of any sugar moiety. The moiety derived from a sugar may be attached to boron by any two of the hydroxyl groups of the sugar. For example, in various embodiments, the boronate ester forms a 5-, 6-, 7-, 8-, or 9-membered ring. In some preferred embodiments, the boronate ester forms a 5- or 6-membered ring.
The sugar is preferably a monosaccharide or disaccharide. Non-limiting examples of suitable sugars include, glucose, sucrose, fructose, trehalose, mannitol, and sorbitol. In certain preferred embodiments, the sugar is a reduced sugar, more preferably mannitol or sorbitol. Thus, in the embodiment wherein the sugar is mannitol or sorbitol, Z1 and Z2 together form a moiety of formula C6H12O6, wherein the oxygen atoms of the two deprotonated hydroxyl groups form covalent attachments with boron to form a boronate ester compound.
Preferably, the mannitol or sorbitol boronate ester compound has one of the following structures: 
However, structures with larger boronate ester ring sizes are also possible.
In certain preferred embodiments, the mannitol or sorbitol boronate ester forms a symmetrical 5-membered ring having the following structure: 
Preferably, the mannitol or sorbitol is of the D-configuration, although the L-configuration may also be used. In certain particularly preferred embodiments, Z1 and Z2 together form a moiety derived from D-mannitol. In these embodiments, the boronate ester compound preferably has one of the following structures: 
However, structures with larger boronate ester ring sizes are also possible.
In certain particularly preferred embodiments, the boronate ester compound has the following structure: 
The P moiety of the compound of formula (1) is preferably hydrogen or one of R7xe2x80x94C(O)xe2x80x94, R7xe2x80x94S(O)2xe2x80x94, R7xe2x80x94NHxe2x80x94C(O)xe2x80x94, or R7xe2x80x94Oxe2x80x94C(O)xe2x80x94, where R7 is one of alkyl, aryl, alkaryl, or aralkyl, any of which can be optionally substituted, or when Y is R7xe2x80x94C(O)xe2x80x94 or R7xe2x80x94S(O)2xe2x80x94, R7 can also be an optionally substituted 5- to 10-membered saturated, partially unsaturated, or aromatic heterocycle.
In certain preferred embodiments, P is one of R7xe2x80x94C(O)xe2x80x94 or R7xe2x80x94S(O)2xe2x80x94, and R7 is an optionally substituted 5- to 10-membered saturated, partially unsaturated, or aromatic heterocycle. Preferably, R7 is an aromatic heterocycle, more preferably pyrazinyl, pyridyl, quinolyl, or quinoxalinyl, or a saturated heterocycle, preferably morpholinyl. In some preferred embodiments, P is (2-pyrazine)carbonyl or (2-pyrazine)sulfonyl.
In some preferred embodiments, R is hydrogen. In some other preferred embodiments, R is alkyl, preferably C1-C6 alkyl, more preferably C1-C4 alkyl, and most preferably methyl or ethyl.
The variable A in formula (1) can be 0, 1, or 2. Thus, when A is zero, the residue within the brackets is not present and the boronate ester compound is a dipeptide. Similarly, where A is 1, the residue within the brackets is present and the compound is a tripeptide. Where A is 2, the compound is a tetrapeptide. In certain particularly preferred embodiments, A is zero. For purposes of the invention, the terms xe2x80x9cpeptidexe2x80x9d, xe2x80x9cdipeptidexe2x80x9d, and xe2x80x9ctripeptidexe2x80x9d are intended to encompass compounds comprising natural amino acid residues, unnatural amino acid residues, or a combination of natural and unnatural amino acid residues. It will be apparent from formulae (1)-(3), that the terms xe2x80x9cpeptidexe2x80x9d, xe2x80x9cdipeptidexe2x80x9d, and xe2x80x9ctripeptidexe2x80x9d are used herein to refer to compounds in which the carboxylic acid functionality of the C-terminal amino acid residue is replaced by a boronic acid or boronate ester functionality.
It is preferred that the substituents R1, R2, and R3 in formula (1) are each independently one of hydrogen, C1-C8 alkyl, C3-C10 cycloalkyl, or C6-C10 aryl, or xe2x80x94CH2xe2x80x94R5, wherein each of R1, R2, R3, and R5 may be optionally substituted. More preferably, R1, R2, and R3 are each independently one of C1-C4 alkyl or xe2x80x94CH2xe2x80x94R5, and R5 is one of cycloalkyl, aryl, heterocyclyl, heteroaryl, or xe2x80x94Wxe2x80x94R6 where W is chalcogen and R6 is alkyl. Preferably, R5 is one of C6-C10 aryl, (C6-C10)ar(C1-C6)alkyl, (C1-C6)alk(C6-C10)aryl, C3-C10 cycloalkyl, C1-C8 alkoxy, or C1-C8 alkylthio or a 5- to 10-membered heteroaryl ring.
In certain preferred embodiments, the compound of formula (1) is one of:
D-Mannitol N-(2-pyrazine)carbonyl-L-phenylalanine-L-leucine boronate;
D-Mannitol N-(2-quinoline)sulfonyl-L-homophenylalanine-L-leucine boronate;
D-Mannitol N-(3-pyridine)carbonyl-L-phenylalanine-L-leucine boronate;
D-Mannitol N-(4-morpholine)carbonyl-L-phenylalanine-L-leucine boronate;
D-Mannitol N-(4-morpholine)carbonyl-xcex2-(1-naphthyl)-L-alanine-L-leucine boronate;
D-Mannitol N-(8-quinoline)sulfonyl-xcex2-(1-naphthyl)-L-alanine-L-leucine boronate;
D-Mannitol N-(4-morpholine)carbonyl-(O-benzyl)-L-tyrosine-L-leucine boronate;
D-Mannitol N-(4-morpholine)carbonyl-L-tyrosine-L-leucine boronate; or D-Mannitol N-(4-morpholine)carbonyl-[O-(2-pyridylmethyl)]-L-tyrosine-L-leucine boronate.
In certain particularly preferred embodiments, the compound of formula (1) is D-Mannitol N-(2-pyrazine)carbonyl-L-phenylalanine-L-leucine boronate, preferably having the following structure: 
In a second aspect, the invention provides a composition comprising a compound of formula (2): 
wherein
P is hydrogen or an amino-group-protecting moiety;
R is hydrogen or alkyl;
A is 0, 1, or 2;
R1, R2, and R3 are independently hydrogen, alkyl, cycloalkyl, aryl, or xe2x80x94CH2xe2x80x94R5;
R5, in each instance, is one of aryl, aralkyl, alkaryl, cycloalkyl, heterocyclyl, heteroaryl, or xe2x80x94Wxe2x80x94R6, where W is a chalcogen and R6 is alkyl;
where the ring portion of any of said aryl, aralkyl, alkaryl, cycloalkyl, heterocyclyl, or heteroaryl in R1, R2, R3 or R5 can be optionally substituted; and
Z3 and Z4 together form a moiety derived from a compound having at least two hydroxyl groups separated by at least two connecting atoms in a chain or ring, said chain or ring comprising carbon atoms and, optionally, a heteroatom or heteroatoms which can be N, S, or O, wherein the atom attached to boron in each case is an oxygen atom;
in a lyophilized powder.
Preferred values for the variables P, R, A, R1, R2, R3, R5, and R6 according to this aspect of the invention are as described above for the first aspect.
The term xe2x80x9cmoiety derived from a compound having at least two hydroxyl groupsxe2x80x9d according to this aspect of the invention is used analogously to the term xe2x80x9cmoiety derived from a sugarxe2x80x9d described above, and thus refers to a moiety formed by removing the hydrogen atoms from two hydroxyl groups of a compound having at least two hydroxyl groups. The moiety derived from a compound having at least two hydroxyl groups may be attached to boron by the oxygen atoms of any two of its hydroxyl groups. Preferably, the boron atom, the oxygen atoms attached to boron, and the atoms connecting the two oxygen atoms together form a 5- or 6-membered ring. Examples of suitable compounds having at least two hydroxyl groups (xe2x80x9cdihydroxy compoundsxe2x80x9d) include, without limitation, pinanediol, pinacol, perfluoropinacol, ethylene glycol, diethylene glycol, catechol, 1,2-cyclohexanediol, 1,3-propanediol, 2,3-butanediol, 1,2-butanediol, 1,4-butanediol, glycerol, and diethanolamine.
For purposes of the present invention, the dihydroxy compound is preferably pharmaceutically acceptable and is preferably miscible or soluble in water or an alcoholic solvent. In some preferred embodiments, the dihydroxy compound is a sugar, as described above, preferably a monosaccharide or disaccharide, more preferably a reduced sugar, and most preferably sorbitol or mannitol. In certain particularly preferred embodiments, the dihydroxy compound is mannitol, most preferably D-mannitol.
The composition according to this aspect of the invention is in the form of a lyophilized powder. In some preferred embodiments, the composition also comprises the free dihydroxy compound. Preferably, the dihydroxy compound and the compound of formula (1) are present in the mixture in a molar ratio ranging from about 0.5:1 to about 100:1, more preferably from about 5:1 to about 100:1. In various embodiments, the dihydroxy compound and the compound of formula (1) are present in a ratio ranging from about 10:1 to about 100:1, from about 20:1 to about 100:1, or from about 40:1 to about 100:1.
In some preferred embodiments, the composition further comprises one or more other pharmaceutically acceptable excipients, carriers, diluents fillers, salts, buffers, stabilizers, solubilizers, and other materials well known in the art. The preparation of pharmaceutically acceptable formulations containing these materials is described in, e.g., Remington: The Science and Practice of Pharmacy, 20th Ed., ed. A. Gennaro, Lippincott Williams and Wilkins, 2000.
The compounds and compositions according to the first and second aspects of the invention may be prepared by the methods described herein, or by any method suitable to produce the compound or composition. For example, the boronate esters of formula (1) can be prepared from the corresponding boronic acids by lyophilization in the presence of mannitol or sorbitol, as described herein, or, alternatively, can be prepared from another boronate ester by transesterification. Alternatively, the boronate esters of formula (1) can be prepared by incorporation of the sugar moiety at an earlier stage in the synthesis.
In a third aspect, the invention provides a method for formulating a boronic acid compound, the method comprising:
(a) preparing an aqueous mixture comprising
(i) a boronic acid compound; and
(ii) a compound having at least two hydroxyl groups separated by at least two connecting atoms in a chain or ring, the chain or ring comprising carbon atoms, and optionally, a heteroatom or heteroatoms which can be N, S, or O; and
(b) lyophilizing the mixture.
In certain preferred embodiments, the aqueous mixture comprises one or more co-solvents in addition to water. Preferably, the co-solvent is miscible with water. More preferably, the co-solvent is an alcohol, including, without limitation, ethanol and tert-butanol. The composition of the solvent mixture may range from about 5% to about 95% v/v alcohol. In some embodiments, the aqueous solvent mixture comprises from about 30% to about 50% alcohol, preferably from about 35% to about 45% alcohol. In certain preferred embodiments, the aqueous solvent mixture comprises about 40% tert-butanol.
In some other embodiments, the aqueous solvent mixture comprises from about 1% to about 15% alcohol, preferably from about 5% to about 10% alcohol. In certain preferred embodiments, the aqueous solvent mixture comprises from about 5% to about 10% ethanol.
Preferably, the compound having at least two hydroxyl groups and the boronic acid compound are present in the mixture in a molar ratio ranging from about 1:1 to about 100:1. In various embodiments, the molar ratio of dihydroxy compound to boronic acid compound is about 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, or 100:1. Other ratios are also possible. These ratios are approximate, and may vary somewhat for weighing ease. For example, in the formulation described in Example 1 below, the aqueous mixture contained dihydroxy compound and boronic acid compound in a 10:1 w/w ratio, which corresponds to a 21:1 molar ratio.
The aqueous mixture can be prepared by any order of addition. For example, in some embodiments, the dihydroxy compound is added to an aqueous mixture comprising a boronic acid compound. In some other embodiments, the boronic acid compound is added to an aqueous mixture comprising a dihydroxy compound. In still yet other embodiments, the boronic acid compound and dihydroxy compound can be added at the same time, or nearly at the same time. In some embodiments, it may be advantageous initially to add the boronic acid compound and/or the dihydroxy compound to a solvent mixture containing a higher percentage of co-solvent than is desired for the lyophilization step, and then dilute with water.
In some preferred embodiments, the mixture further comprises one or more pharmaceutically acceptable excipients, carriers, diluents fillers, salts, buffers, stabilizers, solubilizers, and other materials well known in the art. The preparation of pharmaceutically acceptable formulations containing these materials is described in, e.g., Remington: The Science and Practice of Pharmacy, 20th Ed., ed. A. Gennaro, Lippincott Williams and Wilkins, 2000.
Preferred compounds having at least two hydroxyl groups (xe2x80x9cdihydroxy compoundsxe2x80x9d) according to this aspect of the invention are as described above for the second aspect.
In certain preferred embodiments, the boronic acid compound according to this aspect of the invention has formula (3): 
wherein
P is hydrogen or an amino-group-protecting moiety;
R is hydrogen or alkyl;
A is 0, 1, or 2;
R1, R2, and R3 are independently hydrogen, alkyl, cycloalkyl, aryl, or xe2x80x94CH2xe2x80x94R5;
R5, in each instance, is one of aryl, aralkyl, alkaryl, cycloalkyl, heterocyclyl, heteroaryl, or xe2x80x94Wxe2x80x94R6, where W is a chalcogen and R6 is alkyl;
where the ring portion of any of said aryl, aralkyl, alkaryl, cycloalkyl, heterocyclyl, or heteroaryl in R1, R2, R3 or R5can be optionally substituted; and
Z5 and Z6 are each OH.
Preferred values for the variables P, R, A, R1, R2, R3, R5, and R6 according to this aspect of the invention are as described above for the first aspect.
In certain particularly preferred embodiments, the boronic acid compound is one of:
N-(2-pyrazine)carbonyl-L-phenylalanine-L-leucine boronic acid;
N-(2-quinoline)sulfonyl-L-homophenylalanine-L-leucine boronic acid;
N-(3-pyridine)carbonyl-L-phenylalanine-L-leucine boronic acid;
N-(4-morpholine)carbonyl-L-phenylalanine-L-leucine boronic acid;
N-(4-morpholine)carbonyl-xcex2-(1-naphthyl)-L-alanine-L-leucine boronic acid;
N-(8-quinoline)sulfonyl-xcex2-(1-naphthyl)-L-alanine-L-leucine boronic acid;
N-(4-morpholine)carbonyl-(O-benzyl)-L-tyrosine-L-leucine boronic acid;
N-(4-morpholine)carbonyl-L-tyrosine-L-leucine boronic acid; or
N-(4-morpholine)carbonyl-[O-(2-pyridylmethyl)]-L-tyrosine-L-leucine boronic acid.
In a fourth aspect, the invention provides a method for formulating a boronic acid compound, the method comprising:
(a) preparing a boronic acid anhydride compound;
(b) mixing the boronic acid anhydride compound with water and a compound having at least two hydroxyl groups separated by at least two connecting atoms in a chain or ring, the chain or ring comprising carbon atoms, and, optionally, a heteroatom or heteroatoms which can be N, S, or O to produce an aqueous mixture; and
(c) lyophilizing the mixture.
For purposes of the invention, the term xe2x80x9cboronic acid anhydridexe2x80x9d refers to a chemical compound formed by combination of two or more molecules of a boronic acid compound of formula (3), with loss of one or more water molecules from the boronic acid moieties. When mixed with water, the boronic acid anhydride compound is hydrated to release a free boronic acid compound of formula (3).
In various embodiments, the boronic acid anhydride structure can comprise two, three, four, or more boronic acid units and can have a cyclic or linear configuration. In some embodiments, the boronic acid anhydride compound exists substantially in a single oligomeric form. However, the term xe2x80x9cboronic acid anhydride compoundxe2x80x9d also encompasses mixtures of different oligomeric boronic acid anhydrides.
Non-limiting examples of such oligomeric boronic acid anhydrides are illustrated below: 
In formulae (4) and (5), n is an integer from 0 to about 10, preferably 0, 1, 2, 3, or 4. W, at each occurrence, preferably has formula (6): 
wherein P, R1, R2, R3, and A are as defined above for formulae (1)-(3). In some preferred embodiments, the boronic acid anhydride compound comprises a cyclic trimer (xe2x80x9cboroxinexe2x80x9d) of formula (5), wherein n is 1 and W has the meaning given above.
In some embodiments, at least 80% of the boronic acid present in the boronic acid anhydride compound exists in a single oligomeric anhydride form. In some embodiments, at least 85%, 90%, 95%, or 99% of the boronic acid present in the boronic acid anhydride compound exists in a single oligomeric anhydride form. In some embodiments, the boronic acid anhydride compound consists essentially of a single oligomeric boronic acid anhydride. In some embodiments, the boronic acid anhydride compound consists of a single oligomeric boronic acid anhydride.
In some preferred embodiments, the boronic acid anhydride compound consists of, or consists essentially of, a boroxine of formula (5), wherein n is 1, and W has the meaning given above. In certain particularly preferred embodiments, the boronic acid anhydride compound consists of, or consists essentially of, a boroxine having formula (7): 
The boronic acid anhydride compound preferably can be prepared from the corresponding boronic acid compound of formula (3) by exposure to dehydrating conditions, including, but not limited to, recrystallization, lyophilization, exposure to heat, and/or exposure to a drying agent. Nonlimiting examples of suitable recrystallization solvents include ethyl acetate, dichloromethane, hexanes, ether, acetonitrile, ethanol, and mixtures thereof.
In a fifth aspect, the invention provides compositions prepared according to the methods of the third or fourth aspects of the invention. In some preferred embodiments, formulation of a boronic acid according to the methods of the invention results in formation of a chemical derivative of the boronic acid compound, preferably formation of a boronate ester. In these embodiments, formulation of a boronic acid compound according to the method of the invention produces a composition comprising a boronate ester compound, according to the second aspect of the invention.
In some other embodiments, formulation of a boronic acid compound according to the method of the invention does not result in formation of a chemical derivative of the boronic acid compound. In these embodiments, the composition according to the fifth aspect of the invention comprises a boronic acid compound and a compound having at least two hydroxyl groups in a lyophilized powder.
The compositions according to the second and fifth aspects of the invention can be readily reconstituted by adding an aqueous solvent. Preferably, the reconstitution solvent is suitable for pharmaceutical administration. Examples of suitable reconstitution solvents include, without limitation, water, saline, and phosphate buffered saline (PBS). For clinical use, the compositions according to the second or fifth aspects of the invention are preferably reconstituted with sterile saline (0.9% w/v).
Upon reconstitution in aqueous medium, an equilibrium is established between any boronate ester present in the composition and the corresponding boronic acid. Typically, equilibrium is reached quickly, e.g., within 10-15 minutes, after the addition of water. The relative concentrations of boronate ester and boronic acid present at equilibrium is dependent upon the pH of the solution, temperature, and the ratio of dihydroxy compound to boronic acid compound.
In a sixth aspect, the invention provides a boronic acid anhydride compound useful for the methods of the invention. Preferred boronic acid anhydride compounds are as described above for the fourth aspect of the invention. When mixed with water, the boronic acid anhydride compound is hydrated to release the free boronic acid.
The following examples are intended to further illustrate certain preferred embodiments of the invention, and are not intended to limit the scope of the invention.